Short-Stroke verses Long-Stroke Gas Pistons

[Precision]

From what I understand, the SS was designed for the AR-15 and the LS was designed for the AK. The SS sounds like it would provide a more stable/controllable rifle, but the long-stroke sounds like a slightly more reliable system. I have no experience with either, so I can't say anything about recoil, durability, or accuracy.

I've seen AKs fired in slow motion, and it's NOT a pretty sight. Lots of violent movements. Looks like the whole gun is gonna fall apart. I think this is due to the fact that the LS utilizes such a long travel time for the piston.

Violent movement number 1: gun is fired.
Violent movement number 2: piston travels all the back and collides with the end of the buffer assembly (if this is the incorrect term I apologize).
Violent movement number 3: it begins its journey back to its original position, and the process starts over again. Robust, but that's the only upside.

Doesn't make for a controllable weapon, in my opinion. The SS utilizes a shorter piston travel, but I guess that means that you're gonna have more reliability issues, such as the bolt not moving back all the way and resulting in a jam. I really can't rely on personal experience with pistons, so I wondered if anyone has done a comparison or ones SS and LS.

Thanks guys!

 

[Bartholomew Roberts]

http://en.wikipedia.org/wiki/Gas-operated_reloading

From what I understand, the SS was designed for the AR-15

No, this is incorrect. The AR15 is not a short-stroke gas operated piston. It is a direct impingement gas system. Also, the short-stroke gas piston method of reloading a firearm predates the AR15.

 

[Precision]

I know the AR was ORIGINALLY designed for the AR-15, but I was under the impression that the SS was later designed to compliment that in other similar guns like the HK416. apparently i was wrong?

 

[Ian]

The first example that jumps to mine of a pre-AR short stroke design is the M1 Carbine. Long-stroke piston designs date back to the very earliest semi-auto rifles, like the clunky conversions of existing bolt guns by clapping a big piston onto the side to operate the bolt. Direct gas impingement also predates the AR; it was used in the Swiss AG-42 Ljungman, among others. The many-lug rotating bolt came straight from Melvin Johnson.

The AR's innovation lay mostly in the use of aluminum and plastic, not in mechanical design.

 

[Tommygunn]

Doesn't make for a controllable weapon, in my opinion. The SS utilizes a shorter piston travel, but I guess that means that you're gonna have more reliability issues, such as the bolt not moving back all the way and resulting in a jam.

I have a M-1 Carbine and aside from it not liking hollowpoint rounds it is a very reliable and a very controllable weapon. If the bolt was not moving all the way back I would suspect the tappet housing was dirtied up, but this is not a problem the carbine exhibits in any great numbers. There are possible other reasons for short-stroking though.

I have no experience with the Garand, but it was praised very highly by General Patton and millions of WW2 servicemen liked it, so I will express the opinion it, too, was a very reliable weapon with a long stroke piston and a more powerful cartridge.

 

[benEzra]

The SKS and FAL are short-stroke systems as well. The distinction, of course, is that the short-stroke piston/op rod isn't attached to the bolt carrier, and the long-stroke piston is.

The AK's reliability has as much to do with the very long stroke of the bolt carrier, the awesomely reliable (but extremely heavy) magazines, and the very roomy receiver with lots of open space around the bolt carrier. The attached piston simplifies things mechanically and helps keep the bolt carrier from tilting, but there is no fundamental reason why a short-stroke piston or DI system couldn't be as reliable.

Personally, I can't tell much difference between firing an SKS (short-stroke piston) and an AK (long-stroke piston); the differences due to barrel length, rifle weight, and buttplate area are much more pronounced, IMO. Nor have I had the opportunity to fire an AK in .223 or 5.45x39, so I can't really compare one to the AR (7.62x39mm is obviously harder recoiling, but that's largely a momentum issue due to the larger bullet mass).

Another thing that makes the AR very gentle to shoot (in addition to the straight-line DI system) is the ingenious buffer setup, which uses loose weights inside the hollow buffer sort of like a dead-blow hammer. It has damping ability that a solid buffer of equivalent weight completely lacks, and helps prevent bolt carrier bounce among other things.

 

[iamkris]

Also you are incorrect in associating the slo-mo videos of the AK rattling around with a long sroke piston. Those are independent of wach othera

 

[benEzra]

Regarding the rattling around thing, keep in mind that the cleaning rod bounce seen in the (in)famous Discovery Channel video is just that---the cleaning rod bouncing. There may be a tiny bit of barrel flex visible caused by the piston launch, but it's hard to tell.

 

[elmerfudd]

Regarding the rattling around thing, keep in mind that the cleaning rod bounce seen in the (in)famous Discovery Channel video is just that---the cleaning rod bouncing. There may be a tiny bit of barrel flex visible caused by the piston launch, but it's hard to tell.

Spot on! That's really one of the worst videos out there.

As benEzra mentioned, the flex you see in that video, (virtually everyone knows that video), is actually the cleaning rod bending giving the optical illusion of the barrel bending. I actually paused the video in several places and held a straightedge up to the screen to verify this.

The misinformation doesn't end there though. AK's are MUCH more accurate than what was portrayed in the video. In the hands of competent shooters, AK's have no problem whatsoever keeping all their shots on paper at 200 yards. True, they're not as accurate as AR's, but they're very capable of hitting a human silhouette out to 300 yards and with a capable marksman pulling the trigger, they can do it every time.